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AGNT40 KWNM 251201

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
701 AM EST Sat Feb 25 2017

.FORECAST DISCUSSION...Major features/winds/seas/significant
.weather for the North Atlantic Ocean W of 50W from 30N to 50N.

A weak low pressure center over the outer central NT2 waters
continues to lift Nwd and likely has max associated winds up to
25 or 30 kt over its E semicircle. Max associated seas over its E
semicircle and likely in the low teens which are being handled
equally well by the 06Z Wavewatch III and 00Z ECMWF WAM models at
the moment.

Over the short term, the latest models remain in good agreement
that the surface low will continue to lift Nwd today and then get
absorbed tonight by a fairly strong cold front racing SE across
the offshore waters. With the 06Z GFS remaining very consistent,
will continue to use the previously populated mix of 00Z GFS
winds for this fropa with no major changes to the previously
forecasted associated gale warnings (primarily from the gulf
stream Swd in the NT2 waters tonight and then the Gulf of Maine

In the long range, with marginally unstable forecast to still be
in place, per the 06Z GFS it looks close as to whether WSW gales
will develop in the Gulf of Maine for a brief period on Mon in
advance of a weak cold front. For now would compromise with the
weaker 00Z GFS/ECMWF solutions and will keep winds subgale (up to
25-30 kt). Then further out in the long range, based on the zonal
upper level flow forecasted, would favor the weaker 06Z/00Z GFS
and 00Z ECMWF solutions, versus the 00Z GEM/NAVGEM/UKMET, for a
warm front to lift slowly Nwd across the NT2 then NT1 waters Tue
into Wed, followed by a cold front approaching the E coast Wed
night which will result in a strengthening Sly gradient
developing throughout the coastal/offshore waters. The previous
mix of 00Z GFS and 00Z ECMWF winds for this Sly gradient still
looks representative, with gales possible primarily in the
vicinity of the gulf stream in the NT2 waters Wed night. So will
continue to use these winds for the next offshore forecast
package with just some minor additional edits in deference to the
06Z GFS.


A much more active, and more typical weather pattern for late
February and early March is forecast to develop over the region
during the next several days.

Over the short term, the 06Z preliminary NCEP surface analysis
shows a 1007 MB low pressure area just south of the southeastern
NT2 waters, or near 30N 74W, moving north and northeast. A late
evening ASCAT pass indicated gales associated with this low
occurring east of the southern NT2 offshore waters, or about 60
NM west of Bermuda. Gales associated with the low will likely
remain east of the offshore waters today as the low tracks off
to the northeast, and passes near and just east of the NT2
waters, reaching Georges Bank tonight. There will be showers and
a chance of thunderstorms over mainly eastern NT2 waters today
closer to the low. The next main weather feature that will
likely bring a period of gales to central and northern NT2
waters tonight, and then northern NT1 waters Sunday into Sunday
night, is a strong cold front. This front is still forecast to
move offshore later today, then cross the waters tonight. There
will be a threat for thunderstorms ahead of the front from NT1
waters southward into NT2 waters by later today and tonight.
Local wind gusts exceeding gale force and very rough seas can be
found in and near any of the heavier thunderstorms. Strong cold
air advection moving over the warmer waters of the Gulf Stream
tonight will help to enhance winds and allow for a period of
gale force winds over mainly central into northern NT2 waters.
A stronger pressure gradient between low pressure over southeast
Canada and high pressure building east toward the southeast U.S.
behind the front will lead to gales over the Gulf of Maine
Sunday into early Sunday night. Conditions will improve Sunday
into Sunday night from southwest to northeast over the area as
high pressure builds east into NT2 waters. The 00Z models are in
very good agreement over the region through Sunday night. We
will rely on the 00Z GFS, and use the smart tool which places
the stronger first sigma layer winds over unstable areas and
lower 10 meter winds over the more stable areas today through
Sunday night. Confidence levels are above average through the
short term part of the forecast.

Over the long term, the 00Z global models are coming into better
agreement, leading to confidence levels that are near average.
High pressure will pass to the east of the NT2 waters during
Monday as a weak cold front passes southeast over northeast NT1
waters later Monday into Monday night. A weak high pressure
ridge will then form over NT1 waters by early Tuesday. The ridge
will move east of the region by Tuesday night as a warm front
forms along the mid-Atlantic coast. The front will be slow to
lift north during Wednesday as weak low pressure areas form and
track east along the boundary. A stronger low is forecast to
move east from the Great lakes later Wednesday, and pass over
New England Wednesday night. A strong south and southwest wind
field is likely ahead of a strong cold front by Wednesday night,
with a better chance for gales developing over mainly NT2 waters
at that time. The front will move east into the waters by later
Wednesday night. Overall, the 00Z models remain in pretty decent
agreement over the region Monday through Wednesday night. For
the early morning package we will remain close to the 00Z GFS
for Monday through Tuesday night, and with no significant
weather systems impacting the waters during this time period
rely on the GFS 10 meter winds. For Wednesday and Wednesday
night, we will use a blend of the 00Z GFS and 00Z ECMWF models,
boosting the ECMWF winds by up to 15 percent. Additional
adjustments to the added gale force winds possible for Wednesday
night over NT2 waters can be expected over the next few days.

As for the seas, the 00Z Wavewatch and ECMWF WAM are well
initialized over and near the offshore waters based on the
current observations and altimeter data. Sea heights range from
near 15 feet east of the southern NT2 waters to 3 feet or so just
off the northern mid-Atlantic and New England coasts. Both models
remain in decent agreement through most of the forecast period.
We will, therefore, use a 50/50 blend of these two solutions
through Wednesday night.



.NT1 New England Waters...
.ANZ800...Gulf of Maine...
     Gale Sunday into Sunday night.

.NT2 Mid-Atlantic Waters...
.ANZ915...Hudson Canyon to the Great South Channel...
     Gale Possible Wednesday night.
.ANZ920...Baltimore Canyon to the Great South Channel...
     Gale tonight.
     Gale Possible Wednesday night.
.ANZ910...East of the Great South Channel and south of 39N...
     Gale tonight.
     Gale Possible Wednesday night.
.ANZ828...Inner Waters from Cape Charles Light to Currituck Beach Light...
     Gale Possible Wednesday night.
.ANZ925...Outer Waters from Baltimore Canyon to Hatteras Canyon...
     Gale tonight.
     Gale Possible Wednesday night.
.ANZ830...Inner Waters from Currituck Beach Light to Cape Hatteras...
     Gale tonight.
     Gale Possible Wednesday night.
.ANZ833...Inner Waters from Cape Hatteras to Cape Fear...
     Gale tonight.
     Gale Possible Wednesday night.
.ANZ930...Outer Waters from Hatteras Canyon to Cape Fear...
     Gale tonight.
     Gale Possible Wednesday night.


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